#!/usr/bin/env python

# dbfUtils.py
# By Raymond Hettinger
# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/362715

import struct, datetime, decimal, itertools

def dbfreader(f):
	"""Returns an iterator over records in a Xbase DBF file.

	The first row returned contains the field names.
	The second row contains field specs: (type, size, decimal places).
	Subsequent rows contain the data records.
	If a record is marked as deleted, it is skipped.

	File should be opened for binary reads.

	"""
	# See DBF format spec at:
	#     http://www.pgts.com.au/download/public/xbase.htm#DBF_STRUCT

	numrec, lenheader = struct.unpack('<xxxxLH22x', f.read(32))    
	numfields = (lenheader - 33) // 32

	fields = []
	for fieldno in xrange(numfields):
		name, typ, size, deci = struct.unpack('<11sc4xBB14x', f.read(32))
		name = name.replace('\0', '')       # eliminate NULs from string   
		fields.append((name, typ, size, deci))
	yield [field[0] for field in fields]
	yield [tuple(field[1:]) for field in fields]

	terminator = f.read(1)
	assert terminator == '\r'

	fields.insert(0, ('DeletionFlag', 'C', 1, 0))
	fmt = ''.join(['%ds' % fieldinfo[2] for fieldinfo in fields])
	fmtsiz = struct.calcsize(fmt)
	for i in xrange(numrec):
		record = struct.unpack(fmt, f.read(fmtsiz))
		if record[0] != ' ':
			continue                        # deleted record
		result = []
		for (name, typ, size, deci), value in itertools.izip(fields, record):
			if name == 'DeletionFlag':
				continue
			if typ == "N":
				value = value.replace('\0', '').lstrip()
				if value == '':
					value = 0
				elif deci:
					value = decimal.Decimal(value)
				else:
					value = int(value)
			elif typ == 'D':
				y, m, d = int(value[:4]), int(value[4:6]), int(value[6:8])
				value = datetime.date(y, m, d)
			elif typ == 'L':
				value = (value in 'YyTt' and 'T') or (value in 'NnFf' and 'F') or '?'
			result.append(value)
		yield result


def dbfwriter(f, fieldnames, fieldspecs, records):
	""" Return a string suitable for writing directly to a binary dbf file.

	File f should be open for writing in a binary mode.

	Fieldnames should be no longer than ten characters and not include \x00.
	Fieldspecs are in the form (type, size, deci) where
		type is one of:
			C for ascii character data
			M for ascii character memo data (real memo fields not supported)
			D for datetime objects
			N for ints or decimal objects
			L for logical values 'T', 'F', or '?'
		size is the field width
		deci is the number of decimal places in the provided decimal object
	Records can be an iterable over the records (sequences of field values).
	
	"""
	# header info
	ver = 3
	now = datetime.datetime.now()
	yr, mon, day = now.year-1900, now.month, now.day
	numrec = len(records)
	numfields = len(fieldspecs)
	lenheader = numfields * 32 + 33
	lenrecord = sum(field[1] for field in fieldspecs) + 1
	hdr = struct.pack('<BBBBLHH20x', ver, yr, mon, day, numrec, lenheader, lenrecord)
	f.write(hdr)
					  
	# field specs
	for name, (typ, size, deci) in itertools.izip(fieldnames, fieldspecs):
		name = name.ljust(11, '\x00')
		fld = struct.pack('<11sc4xBB14x', name, typ, size, deci)
		f.write(fld)

	# terminator
	f.write('\r')

	# records
	for record in records:
		f.write(' ')                        # deletion flag
		for (typ, size, deci), value in itertools.izip(fieldspecs, record):
			if typ == "N":
				value = str(value).rjust(size, ' ')
			elif typ == 'D':
				value = value.strftime('%Y%m%d')
			elif typ == 'L':
				value = str(value)[0].upper()
			else:
				value = str(value)[:size].ljust(size, ' ')
			assert len(value) == size
			f.write(value)

	# End of file
	f.write('\x1A')
